Use the same function to initialize the FSFS 'current' file that we
use to update it.

* subversion/libsvn_fs_fs/fs_fs.c
  (svn_fs_fs__create): Manually create the file and then use the util
                       function to write its content.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1629855 13f79535-47bb-0310-9956-ffa450edef68